Subterranean heaters have been used to heat subterranean geological formations in oil production, remediation of contaminated soils, accelerating digestion of landfills, thawing of permafrost, gasification of coal, as well as other uses. Some examples of subterranean heater arrangements include placing and operating electrical resistance heaters, microwave electrodes, gas-fired heaters or catalytic heaters in a bore hole of the formation to be heated. Other examples of subterranean heater arrangements include circulating hot gases or liquids through the formation to be heated, whereby the hot gases or liquids have been heated by a burner located on the surface of the earth. While these examples may be effective for heating the subterranean geological formation, they may be energy intensive to operate.
U.S. Pat. Nos. 6,684,948 and 7,182,132 to Savage propose subterranean heaters which use fuel cells as a more energy efficient source of heat. The fuel cells are disposed in a heater housing which is positioned within the bore hole of the formation to be heated. The fuel cells convert chemical energy from a fuel into heat and electricity through a chemical reaction with an oxidizing agent. The heat generated by the fuel cells is used to elevate the temperature of the formation while the electricity that is generated by the fuel cells is conducted out of the bore hole to be used by electricity consuming devices. While the subterranean heaters of U.S. Pat. Nos. 6,684,948 and 7,182,132 may be effective, the fuel cells need to operate for an extended period of time, which will likely be upwards of several years, in order to liberate all of the oil from the formation. During the extended time of operation, it is likely that some fuel cells will fail and the thermal output of the subterranean heaters will decrease and become inefficient or ineffective. While it would be desirable to repair or replace the fuel cells that have failed, repair or replacement of the fuel cells is not possible because the fuel cells are not retrievable from the bore hole after being placed since the subterranean heaters typically extend several hundred feet to in excess of one thousand feet into the formation. Furthermore, the fuel cells cannot be repurposed to a new location after all of the oil has been liberated from the formation.
U.S. patent application Ser. No. 14/013,708 to Fischer et al., the disclosure of which is incorporated herein by reference in its entirety, teaches a subterranean or geothermic heater which uses a combination of fuel cells and combustors to heat a geological formation. The fuel cells and combustors are disposed in a heater housing in an alternating pattern and are operated to heat the heater housing, and consequently the geological formation. The combustors combust a mixture of anode exhaust and cathode exhaust from the fuel cells to produce a heated combustor exhaust which together with the heat produced by the fuel cells heat the geological formation. While the arrangement of Ser. No. 14/013,708 may be effective, the same problems as with U.S. Pat. Nos. 6,684,948 and 7,182,132 may arise since the fuel cells are located in the bore hole just as with the subterranean heaters of U.S. Pat. Nos. 6,684,948 and 7,182,132 as described above.
What is needed is a heater which minimizes or eliminates one of more of the shortcomings as set forth above.